Alleles segregate during gamete formation, but do they do it independently?

Two-factor Cross, F1

RRYY x rryyRound/yellow peas wrinkled/green

What will offspring look like?

Gives hybrid plants needed for next cross

Two-Factor Cross, F2

RrYy x RrYy

Independent Assortment

•Genes for different traits can segregate independently during the formation of gametes.

•Leads to genetic variation in plants, animals, and other organisms.

Not all genes show simple patterns of dominant and

recessive

•Incomplete dominance•Codominance•Multiple alleles•Polygenic traits•Sex-linked

Incomplete Dominance

• One allele NOT dominant over another

• Four o’clock plants

RR x WW

RW

Codominance• Both alleles contribute to the

phenotype

• Chicken: black feathers codom with white

• Heterozygous = erminette (speckled)

• Humans: protein controlling cholesterol levels

• Blood type

Multiple Alleles

• Many genes have more than 2 alleles

• Coat color in rabbits

• Human gene for blood type

Polygenic Traits• Traits controlled by two or more genes

• At least three genes involved in reddish-brown pigment in eyes of fruit flies

• Different combinations of alleles produce different eye colors

• Polygenic traits often show a wide range of phenotypes

• Skin color in humans partly because more than four different genes probably control this trait

Sex-linked Genes